Attempts will be undertaken to purify the solubilized FSH receptor from calf testis. This will be done by application of standard techniques of protein chemistry (gel filtration, ion-exchange chromatography, various types of electrophoresis and affinity chromatography). In parallel studies we will attempt to solubilize testicular adenylate cyclase with the goal of reconstituting, in vitro, a hormonally responsive receptor-adenylate cyclase system, thereby allowing a detailed study of this initial event in the mechanism of action of peptide hormones, at the molecular level. We will also pursue studies on tissue and serum factor which appear to inhibit binding of FSH to testicular receptor in vitro. Our goal here will be to characterize the putative inhibitory substance with regard to chemical nature (peptide, carbohydrate, etc.) and then to obtain evidence that the in vitro effect mentioned above can be duplicated in vivo, possibly resulting in an inhibition of spermatogenesis.